1. Field of the Invention
This invention relates to improvements in a laminated transparent structure including an optical rotation film, and more particularly to such a laminated transparent structure to be used in a head-up display which is configured, for example, such that a driver of an automotive vehicle can observe an image of driving information projected as displaying light on a windshield glass in a manner that the vehicular information is superimposed on the frontal view.
2. Description of the Prior Art
A variety of laminated transparent structures have been hitherto proposed and put into practical use for a head-up display of an automotive vehicle. The laminated transparent structures include those of the type having a reflection film and those having an optically functional film. These laminated transparent structures are configured by directly applying the reflection film on a windshield glass, or by interposing the optically functional film between two glass plates as disclosed in Japanese Patent Provisional Publication No. 2-141720. Another laminated transparent structure has been disclosed in Japanese Patent Provisional Publication No. 5-279090 and Japanese Patent Provisional Publication No. 6-40271 (Japanese Patent Application No. 4-196841).
However, such conventional laminated transparent structures for the head-up display are or may be insufficient in impact resistance and penetration resistance. In view of this, a laminated transparent structure (including the optically functional film) improved in impact resistance and penetration resistance has been proposed as disclosed in Japanese Patent Provisional Publication No. 8-259280 (Japanese Patent Application No. 7-69506). However, this laminated transparent structure has such a tendency that the peripheral section of the optically functional film peels off or deforms owing to deterioration of adhesive (for the film) with age.
Thus, the above-discussed conventional laminated structures cannot meet the requirements of the impact and penetration resistance according to safety regulations such as JIS (Japanese Industrial Standard) No. R3211 (Automotive Vehicle Safety Glass) and R3212 (Automotive Vehicle Safety Glass Testing Method), and insufficient in durability throughout a long time use.